The disclosure relates to a method for state of charge compensation of a battery which has a plurality of battery units.
The disclosure also relates to a method for charging a battery which has a plurality of battery units.
The disclosure also relates to a computer program and a battery management system, which are set up to perform the method, and to a battery and a motor vehicle, the drive system of which motor vehicle is connected to such a battery.
It is known that individual states of charge (SOC) of battery units in a battery pack can drift apart from one another. A method for state of charge compensation of vehicle batteries is known, for example, from DE 10 2008 002 190 A1, wherein the state of charge compensation is performed during the driving operation by, firstly, the state of charge of individual cells being calculated and then, for at least two of said cells, an amount of charge which the cells should discharge being determined. The cells are discharged according to the calculated amount of charge.
A so-called resistive balancing method is also described in DE 10 2009 002 466 A1. In that document, so-called inductive cell balancing is also described as an alternative, wherein the circuit concept for compensation of the cell voltages involves inductive intermediate storage of the electrical energy transported in that case.
The reasons for the states of charge of the battery units drifting apart from one another are, for example, different self-discharge rates of the battery units, different charging efficiencies or different capacities. These effects need not be coupled to one another. It is therefore possible that a battery unit has a high self-discharge during operation, that is to say during discharging, but also has a high charging efficiency during charging, that is to say can take on more charge of the charge current as usable charge than other cells. In this case, the two effects partially compensate for one another by themselves. Present state of charge compensation methods do not take these effects into account and must therefore compensate more charge than necessary.